Nitrogen Supply Influences Herbivore-Induced Direct and Indirect Defenses and Transcriptional Responses in Nicotiana attenuata  

Abstract

Although nitrogen (N) availability is known to alter constitutive resistance against herbivores, its influence on herbivoreinduced responses, including signaling pathways, transcriptional signatures, and the subsequently elicited chemical defenses is poorly understood. We used the native tobacco, Nicotiana attenuata, which germinates in the postfire environment and copes with large changes in soil N during postfire succession, to compare a suite of Manduca sexta-and elicitor-induced responses in plants grown under high-and low-N (LN) supply rates. LN supply decreased relative growth rates and biomass by 35% at 40 d compared to high-N plants; furthermore, it also attenuated (by 39 and 60%) the elicitor-induced jasmonate and salicylate bursts, two N-intensive direct defenses (nicotine and trypsin proteinase inhibitors, albeit by different mechanisms), and carbon-containing nonvolatile defenses (rutin, chlorogenic acid, and diterpene glycosides), but did not affect the induced release of volatiles (cis-a-bergamotene and germacrene A), which function as indirect defenses. M. sexta and methyl jasmonateinduced transcriptional responses measured with a microarray enriched in herbivore-induced genes were also substantially reduced in plants grown under LN supply rates. In M. sexta-attacked LN plants, only 36 (45%) up-regulated and 46 (58%) down-regulated genes showed the same regulation as those in attacked high-N plants. However, transcriptional responses frequently directly countered the observed metabolic changes. Changes in a leaf's sensitivity to elicitation, an attacked leaf's waning ability to export oxylipin wound signals, and/or resource limitations in LN plants can account for the observed results, underscoring the conclusion that defense activation is a resource-intensive response.

Facing the Future of Plant-Insect Interaction Research: Le Retour à la “Raison d'Être”

“…Since the turn of the century, Baldwin and coworkers have developed new molecular techniques to create a genetically manipulable native species, Nicotiana attenuata (Krü gel et al, 2002). Enormous strides have been made with this system (Kessler and Baldwin, 2002), including documentation of the defensive function of herbivore-induced plant volatile emissions in attracting natural enemies and repelling herbivores , trypsin protease inhibitor production (Glawe et al, 2003), and nicotine production , fitness costs of induced resistance (Heil and Baldwin, 2002), herbivore-specific transcriptional responses in plants Baldwin, 2003, 2004), overlapping transcriptional responses to biotic and abiotic stresses (Izaguirre et al, 2003), costs and benefits of proteinase inhibitor production , individual variability in herbivore-specific elicitors (Roda et al, 2004), and impacts of nitrogen availability on defense chemistry (Lou and Baldwin, 2004;Pearse et al, 2006). Species in the Poaceae, i.e.…”

The evolutionary consequences of ecological interactions mediated through phenotypic plasticity

“…Here, the interaction term between abiotic and biotic environmental factors describes how plastic responses to an interaction can vary over different conditions. For example, the capacity of plants to respond to herbivore attack can be affected by nutrient availability (Lou and Baldwin, 2004). Biotic components of the environment include interactions with other organisms and will largely be the focus of the current discussion.…”

Salicylic acid and ethylene signaling pathways are involved in production of rice trypsin proteinase inhibitors induced by the leaf folder Cnaphalocrocis medinalis (Guenée)

“…PIs can be induced by herbivore infestation, pathogen infection or mechanical wounding [11][12][13][14][15][16]. The induced PIs represent either local [7,17] or systemic [18][19][20][21] responses, and either age-dependent [22] or organ-specific [8,18] traits.…”